[409] The age of jet
transportation began on May 5, 1952, with the inauguration of
scheduled service from London to Johannesburg, South Africa. Later
in the year, service was established from London to Ceylon and
from London to Singapore. Then, in April 1953, scheduled flights
were begun from London to Tokyo, a distance of 10 200 miles. The
flying time was 36 hours, as compared with 85 hours for the
propeller-driven aircraft then in use on the route. The pioneering
jet transport that began commercial operations in 1952 was the
DeHavilland Comet 1.

The design of the Comet airliner had its
origins in the waning days of World War II, and the layout of the
aircraft was completed in 1947. The first flight of the prototype
took place on July 27, 1949, with John Cunningham as pilot. The
performance and physical characteristics of the Comet 1A are given
in table
VII, and a three-view drawing of
the [410] aircraft is presented in figure 13.2. A photograph
of a Comet 3, similar in appearance to the Comet 1A, is given in
figure 13.3. The configuration, of the Comet was not significantly
different from that of contemporary long-range propeller-driven
aircraft. A comparison of the characteristics of the Comet given
in table
VII with those of the Lockheed
Constellation given in table III indicates that the Comet was a somewhat lighter
aircraft, had a lower wing loading and a wing of lower aspect
ratio but had a cruising speed of 490 miles per hour at 35 000
feet as compared with 331 miles per hour at 23 000 feet for the
Constellation. The range with maximum payload of 44 passengers was
1750 miles. At a much reduced payload, a range of slightly over
4000 miles was possible. By present-day standards, the Comet 1A
was a small, relatively low performance aircraft. By comparison
with other aircraft of the early 1950's, however, it was extremely
fast.

The Comet 1A was powered with four
DeHavilland Ghost turbojet engines of 5000 pounds thrust each. The
takeoff thrust-to-weight ratio was a very low 0.17. As a
consequence of this low thrust-to-weight ratio, very precise
control over the aircraft attitude was required during the takeoff
roll to prevent overrotation and subsequent high drag and loss of
acceleration. At least one aircraft was lost as a result of
overrotation during takeoff. The four engines were mounted in the
wing roots, two on each side of the fuselage. This engine
arrangement has the advantages of placing the engines near the
longitudinal center-of-gravity position and of minimizing the
asymmetrical yawing moment that accompanies loss of an engine
during takeoff; at the time, it was also thought to be a low-drag
arrangement. The proximity of the engines to each other and to the
passenger cabin, however, posed a possibly hazardous situation in
the event one of the engines disintegrated. Engine disintegration
was a very real concern in 1950. Engine maintenance was also
complicated by the wing-root mounting arrangement.

The aerodynamic design of the wing was
conventional except for the use of 20° of sweepback. The
aspect ratio of 6.6 was low, as compared with contemporary
long-range propeller-driven aircraft. The high-lift system
consisted in a combination of simple plain and split trailing-edge
flaps. Some aircraft employed fences on the wings. The aerodynamic
controls were hydraulically boosted. The passenger cabin was
pressurized to maintain a cabin altitude of 8000 feet at an
aircraft altitude of 40 000 feet.

The Comet I was sold to British, French,
and Canadian airlines, and it appeared that Great Britain had
produced a truly outstanding new aircraft that would be sold in
large numbers throughout the world.

[411] Figure 13.2 - Dehavilland Comet airliner
prototype.

Prospects for the Comet dimmed, however,
when three accidents occurred in which the aircraft disintegrated
in flight. All Comet 1 aircraft, over 20 in number, were withdrawn
from service in 1954. Extensive laboratory studies were undertaken
in an effort to diagnose the problem. Fatigue failure and
subsequent rupture of the pressurized fuselage as a result of
pressure recycling was finally identified as the cause of the
accidents. The Comet was completely reengineered and emerged
as....

[412] Figure 13.3 - DeHavilland Comet 3 airliner.
[David A. Anderton]

....a much changed and improved aircraft in
1958. This version, identified as the Comet 4, was not really
competitive with the new generation of jet transports coming into
use at that time, and only 74 were built.

The commercial success of the Comet was
limited, but it was the first jet transport and represented a
large step forward in our concepts of air transportation and its
utility. It is unfortunate that the pioneering work of the
designers and builders of the Comet was not rewarded with greater
success. The Comet, in highly modified form, survives today as a
marine reconnaissance aircraft known as the Nimrod. An interesting
account of the development of the various versions of the Comet is
contained in reference 169.

The Tupolev Tu- 104 is the second of the
pioneer jet transports. This aircraft was first flown on June 17,
1955, and went into scheduled airline operations in 1956 on the
Moscow-Omsk-Irkutsk route. In 1957, an improved version of the
aircraft, the Tu-104A, captured a number of records for speed,
altitude, distance, and load-carrying capability. The Tu-104
transport was developed from the "Badger" bomber and utilized the
same wings, tall surfaces, engines and inlets, landing gear, and
fuselage nose section as the earlier bomber aircraft. Figure 13.4
depicts a Tu-104B, and the data in table VII are for this version of the aircraft.

As can be seen in figure 13.4, the Tu-104B
is a low-wing aircraft with a conventional tall arrangement and a
wing incorporating pronounced sweepback. The transparent nose
adopted from the bomber version of the aircraft is clearly visible
in the photograph. The two engines that power the Tu-104 are
located in nacelles that are faired into [413] the wing roots.
This arrangement is somewhat similar to that employed on the
Comet; however, the nacelles are larger and the circular inlets
extend forward of the leading edge of the wing, as contrasted with
the leading-edge inlets on the Comet. The two main landing-gear
strutsare fitted with four-wheel bogies and retract
rearward into pods on the wing. The aircraft has a seating
capacity of 100 passengers arranged in a 5-abreast configuration.
The sweepback angle of the aspect ratio 6.5 wing is 40° from
the root to about the midsemispan position and is 37.5° from
there to the tip. Each wing has two large fences located in the
streamwise position on the top surface of each wing. One of these
is at the position where the sweep angle changes, and the other is
farther outboard. As indicated in chapter 10, these fences help control the boundary layer and,
hence, improve the stalling characteristics of the wing. Lateral
control is provided by conventional ailerons that are operated
manually; manual longitudinal control is also used. The rudder is
actuated hydraulically. The wings are equipped with trailing-edge
Fowler-type flaps and have no leading-edge devices. A Fowler flap
is similar to the double-slotted flap shown in figure 10.25(b),
but without the small segment between the wing and the main
portion of the flap.

The Tu-104B is powered by two Mikulin
turbojet engines of 21 385 pounds thrust each. The engines are
equipped with thrust reversers, although some of the early models
did not have this equipment. These early aircraft employed two
braking parachutes to assist in stopping the aircraft on landing.
Insofar as can be determined, no other commercial transport
aircraft (except early versions of the Tupolev...

Figure 13.4 - Tupolev Tu-104B
airliner. [Flt. Intl.]

[414]....Tu-134) has
utilized braking chutes as a routine operational procedure. The
gross weight of the aircraft is 167 551 pounds, which is somewhat
heavier than that of the piston-engine transports at the end of
the era in which these aircraft dominated the world's airlines.
With the large turbojet engines, the thrust-to-weight ratio of the
aircraft, 0.26, is nearly as high as any of the large transports
whose characteristics are given in table VII. The wing loading of 84.8 pounds per square foot is
relatively low compared with more modern designs; however,
comparison of the data given in table VII for different aircraft indicates that the
combination of low wing loading and relatively simple high-lift
devices on the Soviet aircraft give stalling speeds comparable to
those of more modern high performance jet transports.

The range of 1500 miles given in
table
VII for the Tu-104 aircraft with
maximum payload places it in the short-range category. The
cost-economical and maximum cruising speeds are 497 and 590 miles
per hour, respectively; these speeds correspond to Mach numbers of
0.75 at 35 000 feet and 0.85 at 25 000 feet.

The Tu-104 was built in a number of
versions, and some are still in use on domestic routes inside the
Soviet Union. Production of the aircraft ended after 250 units
were constructed. The development history of the Tu-104 series of
aircraft is completely described in reference 190.

Both the DeHavilland Comet and the Tupolev
Tu-104 were pioneers in a new and exciting concept of air
transportation, and both have a well-deserved place in the history
of aeronautical development. In many respects, however, the design
of these aircraft reflected the philosophy of contemporary
propeller-driven aircraft. For example, the low wing loadings,
unsophisticated high-lift devices, and simple control systems are
typical of high-performance propeller-driven transports. The need
for high wing loadings and powerful high-lift
devicesin order to permit cruising at near maximum values
of the lift-drag ratio, but at the same time retaining
satisfactory stalling speeds, is discussed in chapter 3 of
reference 176. The engine location on the Comet and the Tu-104
are no longer used on modern jet transports and must be considered
obsolete for this type of aircraft. The advantages and
disadvantages of mounting the engines in the wing roots are
discussed above in the description of the Comet. This aircraft, as
well as the Tu-104, employed turbojet engines of relatively small
diameter. The beginnings of the high-bypass-ratio turbofan engine
with its large diameter fan poses an additional problem with the
wing-root engine location because of the difficulty of integrating
the large engine into the wing root.